Calls, Loops, and Conditionals

mCallLevel is the macro level in a calling sequence and starts at 0
mLoopLevel is the level of loop and/or if block, starts  at -1 outside blocks
mLoopDepths[mCallLevel] is maintained in tandem with mLoopLevel
mLoopLimit[mLoopLevel] is the loop count to do, or 0 for an unsatisfied IF
or -1 for a satisfied IF
mLoopStart[mLoopLevel]  is the line index of a loop start
mLoopCount[mLoopLevel] is current iteration # of the loop, starts at 1

mCallMacro[mCallLevel] is the macro number being called at a call level
mCallIndex[mCallLevel] is the line index of the CALL statement to be returned
to

When a LOOP is encountered, it increases mLoopLevel, assigns mLoopLimit,
mLoopStart, and mLoopCount, and sets an optional variable

ENDLOOP increases the count and goes back to starting index if not above the
limit, otherwise it clears variables and drops the loop level

When an IF or an ELSEIF in an unsatisfied IF is found, it evaluates the
conditional and increases mLoopLevel for an IF
Then if the condition is NOT satisfied it skips to an ELSE or ENDIF (or
ELSEIF?) and leaves mLoopLimit at 0 to indicate unsatisfied.  If the condition
is satisfied it set mLoopLimit to -1
If it skipped to an ELSE it goes 1 past it so that it will execute, all other
skips are to the point in question

Skipping is done to the requested kind of end by keeping track of if and loop
levels and making sure it matches the respective starting level

Thus an ELSE or ELSEIF is encountered only when the IF is satisfied, and it
unconditionally skips to an ENDIF

BREAK or CONTINUE pop any IFs off the stack by testing for nonpositive
mLoopLimit and decrementing mLoopLevel
and it skips to the ENDLOOP.  BREAK is implemented just by setting the
mLoopCount to mLoopLimit

CALL just increases the mCallLevel after saving the current line index and
saves the new macro number and sets the new loop depth to -1

RETURN pops off any ifs/loops by clearing index variable at each level and
decrementing mLoopLevel until mLoopDepths is -1

Thus the mLoopLevel stack works across calls and returns and loop/if blocks
are not kept track of per macro level.

SKIPTO and labels work by finding the label, counting the net number of
loop levels that it descends, then popping that many IFs/LOOPS.  The checking
for this is hairy because it has to prevent jumps into different block
sections, which are referred to as subblocks.  Every loop, and every component
of IF - ELSEIF -ELSE -ENDIF, is counted as a different subblock at the given
loop level.